1. Field of the Invention
The present invention relates to a honeycomb structure, and a manufacturing method of the honeycomb structure. More particularly, it relates to a honeycomb structure which is a catalyst carrier and also functions as a heater when a voltage is applied thereto, and a manufacturing method of the honeycomb structure.
2. Description of Related Art
Heretofore, a honeycomb structure of cordierite onto which a catalyst is loaded has been used in a treatment of harmful substances in an exhaust gas discharged from a car engine. Moreover, it is known that a honeycomb structure formed of a sintered body of silicon carbide is used in purification of the exhaust gas. When the exhaust gas is treated by the catalyst loaded onto the honeycomb structure, it is necessary to raise a temperature of the catalyst to a predetermined temperature. However, at start of the engine, the catalyst temperature is low, which has caused the problem that the exhaust gas cannot sufficiently be purified.
Thus, there has been suggested a honeycomb structure which is a catalyst carrier and also functions as a heater when a voltage is applied thereto (e.g., see Patent Documents 1 to 4).
In Patent Documents 1 to 3, there is disclosed a honeycomb structure including a tubular honeycomb structure body, and a pair of electrode sections disposed on a side surface of this honeycomb structure body. The honeycomb structure body has porous partition walls to define and form a plurality of cells, and an outer peripheral wall. In Patent Document 1, it is described that a volume electrical resistivity of the honeycomb structure body at 400° C. is from 1 to 40 Ωcm, and a volume electrical resistivity of the electrode sections at 400° C. is 40% or less of the volume electrical resistivity of the honeycomb structure body. In Patent Document 2, electrode sections containing silicon (Si) and silicon carbide (SiC) are described. In the electrode sections of Patent Document 2 an average particle diameter of silicon carbide particles is from 10 to 70 μm, and a ratio (Si/SiC) of a mass between silicon (Si) and silicon carbide (SiC) is from 20/80 to 50/50. Furthermore, in Patent Document 3, it is described that in a cross section perpendicular to a cell extending direction, an angle of 0.5 times a central angle of each electrode section is from 15 to 65°. Further, in Patent Document 3, it is described that each electrode section is formed to be thinner from a central portion in a peripheral direction of the honeycomb structure body toward both ends in the peripheral direction, in the cross section perpendicular to the cell extending direction. Further, in Patent Document 4, there is disclosed a honeycomb body for energization heat generation made of a conductive material, and including a plurality of through holes which are divided by partition walls and are substantially parallel to a gas flow direction, and both end surfaces on a gas inflow side and a gas outflow side. This honeycomb body for energization heat generation further includes electrode sections having a low volume resistivity and a heat generating section having a high volume resistivity, and the electrode sections are formed on both the whole end surfaces. Furthermore, in this honeycomb body for energization heat generation, the volume resistivity of the heat generating section is from 0.1 to 10 Ωcm, and the volume resistivity of the electrode sections is 1/10 or less of the volume resistivity of the heat generating section.    [Patent Document 1] WO 2011/043434    [Patent Document 2] WO 2011/105567    [Patent Document 3] WO 2011/125817    [Patent Document 4] JP-A-2010-229976